This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to developer and toner compositions containing novel crosslinked polyimide resins, and reactive extrusion process for the preparation thereof. In embodiments, there are provided in accordance with the present invention, toner compositions, especially low melting and broad fusing latitude toner compositions, comprised of certain crosslinked polyimide resin and pigment particles, comprised of, for example, carbon black, magnetites, or mixtures thereof, cyan, magenta, yellow, blue, green, red, or brown components, or mixtures thereof thereby providing for the development and generation of black and/or colored images. In embodiments, there are provided in accordance with the present invention crosslinked polyimides obtained from unsaturated polyimide resins of the following formula ##STR2## R represents an aliphatic or oxyaliphatic, especially an alkyl group with 1 to about 25 carbons like methyl, ethyl, butyl, propyl, pentyl, hexyl, octyl, nonyl, stearyl, and the like; and m represents the number of monomer segments, and is, for example, a number of from about 10 to about 1,000. Oxyaliphatic includes those components with from 1 to about 25 carbon atoms, such as methylene oxide, ethylene oxide, propylene oxide, the tripropylene oxide, dipropylene oxide, pentipropylene oxide, tetrapropylene oxide, mixtures thereof, and the like. These aforementioned unsaturated polyimides are then reacted, for example, with peroxides, such as benzoyl peroxide and the like, to provide crosslinked polyimides. Processes for the preparation of the toners of this invention include reactive extrusion process wherein the aforementioned unsaturated polyimide resin is admixed with peroxides such as benzoyl peroxide of about 0.1 percent to about 3 percent by weight of polyimide, and then extruded, for instance, utilizing a Davo Twin extruder operated at a barrel temperature of from about 140.degree. C. to about 180.degree. C., thereby causing the linear unsaturated polyimide to result in crosslinked polyimides. The toner compositions of the present invention in embodiments possess a number of advantages including low melting characteristics, excellent blocking characteristics of above 120.degree. F., possess excellent nonvinyl-offset properties, and low relative humidity sensitivity such as from about 1.2 to about 3.0. The unsaturated polyimides of the present invention can in embodiments be generated by the reaction of at least one alkylene diamine, such as branched JEFFAMINES.TM. available from Texaco Chemicals as JEFFAMINE D-230.TM., D-400.TM., D-700.TM., EDR-148.TM., EDR-192.TM. and believed to be of the following formula ##STR3## The aforementioned unsaturated polyimides exhibit in embodiments a number average molecular weight of from about 3,000 grams per mole to about 100,000, and preferably about 30,000 grams per mole as measured by a vapor phase osmometer, have a glass transition temperature of from about 45.degree. C. to about 65.degree. C., and more preferably of from about 50.degree. C. to about 62.degree. C. as measured by the Differential Scanning Calorimeter.
Examples of advantages of the toner composition of the present invention include low fusing temperatures, such as from about 115.degree. C. to about 145.degree. C., and thus lower fusing energies are required for fixing enabling less power consumption during fusing, and permitting extended lifetimes for the fuser system selected. Furthermore, the toner compositions of the present invention possess in embodiments a broad fusing latitude such as from about 30.degree. C. to about 100.degree. C. with minimal or avoidance of release oil, which inhibits the toner from offsetting onto the fuser rollers usually associated with ghosting or background images on subsequent copies. Additionally, the fused image obtained from the toner compositions of the present invention in embodiments does not substantially offset to vinyl covers, such as those utilized for notebook binders, and possess a low humidity sensitivity ratio of from about 1 to about 2.3 as calculated by the ratio of the triboelectric charge in microcoulombs per gram of the developer after placed in a chamber at 20 percent humidity for 48 hours, to the triboelectric charge in microcoulombs per gram of the developer after placed in a chamber at 80 percent humidity for 48 hours.
For toner resins, it is generally desirable for many uses that the glass transition temperature of the resin be from about 50.degree. C. to about 65.degree. C., and preferably not less than about 55.degree. C., so that the toner particles do not aggregate, coalesce or block during manufacturing, transport storage, or until the toner is required for fixing. Additionally, low fusing toner characteristics are preferred, hence the resin should melt or flow as low in temperature as possible above the glass transition temperature such as from about 1.degree. C. to about 30.degree. C. flow temperature. Moreover, low relative humidity sensitivity of toners is important to the extent that the triboelectric charge is stable to, for example, changes in environmental humidity conditions. Imaging apparatuses, such as xerographic copiers and printers equipped with two component developers, that is a toner as one component mixed with the carrier as the other component can exhibit, for example, a positive or negative triboelectric charge with a magnitude of from about 7 microcoulombs per gram to about 35 microcoulombs per gram as determined by the known Faraday Cage methods. This triboelectric charge of the developer permits the toner particles to be transferred to the latent image of the photoreceptor of opposite charge, thereby forming a toned image on the photoreceptor which is subsequently transferred to a paper or a transparency substrate, and thereafter subjected to fusing or fixing. In many of these development systems, it is important for the triboelectric charge to remain stable under differing environmental humidity conditions such that the triboelectric charge does not change by more than from about 5 to about 10 microcoulombs per gram. A change of more than from about 5 microcoulombs per gram to about 10 microcoulombs per gram in triboelectric charge of the toner developer can, for example, cause nonuniform toned image or cause no toning of the photoreceptor, and thus result in unbalanced image density or gray scale in images, or no images at all. In many climates, humidity ranges may differ of from less than about 20 percent in dry regions to more than about 80 percent in humid regions, and some geographical regions may exhibit fluctuations of up to from about 50 to about 80 percent humidity level within the same day. In these climates, it is desirable that the developmental triboelectric charge does not substantially change by more than from about 5 microcoulombs per gram to about 10 microcoulombs per gram. Since the resins selected for toner can represent, for example, from about 80 percent to about 98 percent by weight of toner, the resin sensitivity to moisture or humidity conditions should be minimized so as to not adversely affect the triboelectric charges. Many polymeric resins utilized as toner compositions, such as for example styrene-acrylates, styrene-methacrylate, styrene-butadiene or polyesters, contain from about 0.1 to about 2 percent by weight of moisture, and in some instances, the moisture contents of the polyester may change from about 0.1 to about 4 percent by weight at humidity levels ranging from about 5 to about 100 percent or, more specifically, from about 20 percent to about 80 percent humidity. These changes in moisture content of the resin may have a dramatic effect in changing the triboelectric charge of the toner developer such as up to about 50 microcoulombs per gram.
Relative humidity sensitivity of toner is customarily measured by first fabricating a toner comprised of a pigment, optionally charge control agent and a resin, and admixing the toner, from about 3 percent by weight to about 7 percent by weight with a carrier, hence generating a toner developer composition. This toner developer composition is then subjected to various humidity levels in a sealed chamber for a finite period of time, such as about 48 hours. The triboelectric charge is then measured for the developer composition at differing humidity levels and evaluated by several methods, such as graphing the triboelectric charge as a function of humidity level and observing the regions in which dramatic changes occur. Another measuring method involves dividing the aforementioned graphical interpolation of tribo vs humidity level in three regions, wherein region 1 is from about 0 to about 30 percent humidity, region 2 is from about above 30 to about 65 percent humidity and region 3 is higher than about 65 percent humidity to about 100 percent. These measurements may be considered cumbersome and time consuming, thus a more practical method in some situations is by measuring the triboelectric charge after subjecting the toner developer composition at two humidity levels such as 20 percent humidity and 80 percent humidity, and then calculating the relative sensitivity by selecting the triboelectric charge ratio of the 20 to 80 percent humidity as follows ##EQU1## wherein RH is the relative humidity.
Thus, if the relative sensitivity is about 1.0, the toner composition is nonhumidity sensitive, whereas if the relative sensitivity is greater than from about 3, or greater than about 5, the toner composition is considered to be very humidity sensitive and may not be as useful in xerographic copiers or printers. It is believed that a number of polymeric materials exhibit relative sensitivity greater than 1.0, and in general, styrene butadiene, or styrene acrylate possess a relative sensitivity of greater than 1.0 and less than about 2.5, whereas polyesters possess a relative sensitivity of greater than 1.8 and less than about 5. Hence, an advantage of the styrene-acrylate or styrene-butadiene class of resins over polyesters is their lower relative sensitivity. Polyesters, however, are known to display advantages over styrene based resins such as in low fixing temperatures of from about 120.degree. C. to about 140.degree. C., high gloss such as from about 50 gloss units to about 80 gloss units, and nonvinyl offset properties. Therefore, there is a need for toner compositions comprised of a resin which possess all of the aforementioned advantages such as low fixing of from about 120.degree. C. to about 140.degree. C., high gloss such as from about 50 gloss units to about 80 gloss units, nonvinyl offset properties and in addition low relative sensitivity such as from about 1.0 to about 2.0. These and other advantages are attained by the toner compositions of this invention comprised of a pigment, optionally a charge control agent and a crosslinked polyimide resin, which toner exhibits in embodiments low fixing of from about 120.degree. to about 140.degree. C., low gloss such as from about 1 gloss units to about 30 gloss units, nonvinyl offset properties and low relative sensitivity such as from about 1.0 to about 2.3. Specifically, in embodiments, the present invention is directed to a toner composition comprised of pigment, charge control agent and certain polyimide resins of the formula illustrated herein, which toners possess low fixing of from about 115.degree. C. to about 145.degree. C., low-gloss such as from about 1 gloss unit to about 30 gloss units as measured by the Gardner Gloss metering unit, nonvinyl offset properties and in addition low relative humidity sensitivity such as from about 1.0 to about 2.0 calculated as illustrated herein and, more specifically, by Equation 1. These and other advantageous are attained by the toners of the invention comprised of a pigment, optionally a charge control agent and, moreover, a crosslinked polyimide resin derived from reacting unsaturated polyimides with a peroxide, such as benzoyl peroxide, and which toner exhibits low fixing of from about 120.degree. C. to about 140.degree. C., low gloss such as from about 1 gloss unit to about 30 gloss units, nonvinyl offset properties and low relative sensitivity such as from about 1.0 to about 2.3.
A number of toner resins are known, such as styrene acrylates, styrene methacrylates, polyesters, polyamides, and generally certain polyimides.
U.S. Pat. No. 5,348,830, illustrates a toner composition comprised of a pigment, and a thermotropic liquid crystalline polyimide of the formula ##STR4## wherein m represents the number of monomer segments present; X is a symmetrical moiety independently selected from the group consisting of phenyl, naphthyl, cyclohexyl, or bicycloaliphatic; and R is independently selected from the group consisting of alkyl, oxyalkylene and polyoxyalkylene.
U.S. Ser. No. 144,956, filed concurrently herewith, illustrates a toner composition comprised of pigment, and polyimide of the formula ##STR5## wherein n represent the number of monomer segments, and is a number of from about 10 to about 1,000; and R is alkyl, oxyalkyl, or polyoxyalkyl.
U.S. Pat. No. 5,348,831 illustrates a toner composition comprised of pigment, and a polyester imide resin of the formula ##STR6## wherein n represent the number of segments present and is a number of from about 10 to about 10,000; R' is alkyl or alkylene; and R is independently selected from the group consisting of an oxyalkylene and polyoxyalkylene.
U.S. Ser. No. 144,918, filed concurrently herewith, illustrates a toner composition comprised of pigment, and polyimide of the formula ##STR7## wherein m, represent the number of monomer segments present; X is ##STR8## thus X can be benzophenone, oxydiphthalic, hexafluoropropane diphenyl, diphenyl sulfone, or biphenyl; and X is attached to four imide carbonyl moieties; and R is independently selected from the group consisting of alkyl, oxyalkylene and polyoxyalkylene.
There are also disclosed in Advances in Polyimides Science in Technology, edited by Cladius Fegere et al., and published by Technomic Publishing (1993), unsaturated polyimides and crosslinked polyimides. However, these unsaturated and crosslinked polyimide resins are aromatic and useful as high performance materials, and there is no teaching therein relating to toners.